An automatic analysis device, which irradiates a reaction mixture obtained by mixing a sample with a reagent with a light from a light source, calculates an absorbance from a change in the amount of a transmitted light with a specific wavelength, and quantitatively determines the concentration of an analyte according to the Lambert-Beer law, has been widely used (for example, PTL 1). In such a device, in a cell disk which repeats rotation and stop, a lot of cells each retaining a reaction mixture are arranged on a circumference thereof, time sequential data on the amount of a transmitted light transmitted through the reaction mixture in the cell is measured as reaction process data at about 15 second intervals for about 10 minutes by a transmitted light measuring section disposed at a given position during the rotation of the cell disk, an absorbance is calculated from a change in light amount, and the concentration of an analyte is quantitatively determined.
As the reaction for which the measurement is performed by the automatic analysis device, there are mainly the following two types of reactions: a color reaction in which a substrate and an enzyme are reacted with each other, and an immune agglutination reaction in which an antigen and an antibody are reacted with each other. An analysis using the former reaction is called a biochemical analysis, and examples of a test item include LDH (lactate dehydrogenase), ALP (alkaline phosphatase), and AST (aspartate-oxoglutarate aminotransferase). An analysis using the latter reaction is called an immunoassay, and examples of a test item include CRP (C-reactive protein), IgG (immunoglobulin), and RF (rheumatoid factor). In an analyte to be measured in the latter reaction, there is a test item requiring quantitative determination in a low concentration range in which the blood concentration is low, and for such a test item, a latex immunoassay in which latex particles having a surface sensitized (bound) with an antibody are used as a sensitizer is used. In the latex immunoassay, an agglutinated body produced by agglutinating the latex particles by an analyte is irradiated with a light, and the amount of a transmitted light transmitted without scattering is measured. The size of the agglutinated body after the lapse of a predetermined time is increased as the concentration of an analyte is increased, and therefore, the concentration of the analyte can be quantitatively determined from a light amount measured as reaction process data.
Recently, it has been demanded that a latex immunoassay have higher sensitivity. A large number of reagents for use in an automatic analysis device have been developed so far, however, there are the following two types of reagents: a reagent for use in a normal analysis and a reagent compatible with a highly sensitive analysis, and a user needs to select a reagent depending on the intended use. Further, as for the device, in order to further increase the sensitivity of the latex immunoassay, it has been tried to measure a scattered light not to measure a transmitted light so far. For example, a system which separates a transmitted light and a scattered light from each other using a diaphragm and simultaneously measures an absorbance and a scattered light (PTL 2), etc. have been disclosed.